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Quasi-identifiers are pieces of information that are not of themselves unique identifiers, but are sufficiently well correlated with an entity that they can be combined with other quasi-identifiers to create a unique identifier.[1]

Quasi-identifiers can thus, when combined, become personally identifying information. This process is called re-identification. Motwani and Ying warn about potential privacy breaches being enabled by publication of large volumes of government and business data containing quasi-identifiers. As an example, neither gender, birth dates nor postal codes uniquely identify an individual, but the combination of all three is sufficient to identify 87% of individuals in the United States.[2]


  1. ^ "Glossary of Statistical Terms: Quasi-identifier". OECD. November 10, 2005. Retrieved 29 September 2013. 
  2. ^ Rajeev Motwani and Ying Xu (2007). "Efficient Algorithms for Masking and Finding Quasi-Identifiers". Proceedings of the Conference on Very Large Data Bases (VLDB). 

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